This invention relates to couplings and, in particular, a coupling between limited axially extendable and translatable members.
A valve actuator coupling is described in the copending application, Ser. No. 663,786 filed on Mar. 4, 1976 in the name of T. E. Kunkle, entitled VALVE-ACTUATOR COUPLING and assigned to the assignee of the present invention, wherein a valve actuator shaft is operatively connected to a valve stem by a coupling which limits valve backseat loading. The coupling includes first and second members, respectively joined to the stem and the actuator, and interconnected at a lost motion connection. The arrangement is such that compressive forces are directly transmitted between the members but, under increasing tensile loading, the members relatively separate and extend as spring means at the lost motion connection are increasingly deflected until the springs are fully deflected. Thereafter, concurrent movement and direct tensile force transmission is effected between the members. In order to prevent full deflection of the Belleville springs, the latter are disposed in series relationship within a counterbore in one member. Under high tensile loads, an annular stop collar engages a stop surface on the other member when the springs are less than fully deflected. In this manner full deflection of the Belleville springs is prevented.
While the aforementioned stop collar limits the deflection of the Belleville springs, certain limitations are present in such a design. For instance, the collar counterbore limits spring diameter for a given coupling diameter. This in turn increases the stress level within the springs for a given loading and deflection. High stresses then make it more imperative that the deflection of the spring be controlled to prevent overdeflection. Further, the annular stop collar is subject to manufacturing inaccuracies and, inasmuch as it directly determines the deflection of the springs, the ultimate load transmission of the coupling affected thereby. In other words, the deflection and load transmission are not solely a function of the spring deflection. Additionally, the mating apexes of the springs in the series design are not self-centering and, should axial or radial misalignment occur, the desired operative relationships are not maintained thereby affecting load transmission characteristics.
The present invention on the other hand, provides a coupling wherein larger sized Belleville springs are disposed in series to provide an extended deflection range with lower stresses limits. The springs have their inner base rims in engagement with a double tapered annular spacer having conical surfaces which directly limit the spring deflection and thereby the ultimate loading thereon. By using the intermediate spacer to directly achieve deflection limitation, the effect of extraneous tolerances are eliminated. Variable deflections can be established by merely substituting spacers with varying conical angles and the loading can be changed by increasing the number of springs providing the coupling has sufficient axial capabilities to accommodate the same without revision of other component parts. The spacer also provides a centering capability for the opposed spring sets to maintain the same in operative relationship in assembly.
To this end, the coupling comprises first and second members which are telescopically journalled for relative axial movement at an annular lost motion connection having axially spaced surfaces. First and second sets of Belleville springs are disposed in the lost motion connection in opposed relation. The springs are separated by the double tapered annular spacer. The arrangement is such that the apex annular surfaces of the inner springs engage spacer while the base rims of the outer springs are initially engageable at low loads with an outer portion of the spacer and increasingly deflect toward the spacer as the tensile loading increases until full engagement is achieved when the springs reach a predetermined deflection and consequently an upper tensile load transmission limit, after which deflection, the members are directly coupled.